Light-tightly packaged rolls are known, wherein a roll of light-sensitive strip material, e.g. photographic film or paper, a polyester printing plate, or another light-sensitive strip material, is wound on a hollow supporting core. Such packaged rolls comprise a light-tight flexible end cover for each end surface of the roll, each end cover having a central opening and being light-tightly attached to a corresponding end of the core, and a light-tight flexible circumferential cover secured to the coiled strip material and covering the outermost convolution of the roll. The peripheral areas of the end covers and the side ends of the circumferential cover are light-tightly fitted to each other so as to obtain a light-tight and/or moisture-tight wrapping.
The flexibility of the end covers causes several problems. In the first place, when dispensing the light-sensitive material, the covers may press against the unwinding light-sensitive material, which results in varying friction forces between the end covers and the light-sensitive material. Because of varying friction, the light-sensitive material is not transported smoothly, but with shocks, through the exposure apparatus. When an image is exposed on the light-sensitive material during transport, image quality suffers from the unsmoothness of transport. This problem will hereinafter be referred to as the "unsmooth transport" problem.
In the second place, the flexible end covers may bend inwards to the core. Thus, when the dispensed light-sensitive material is rewound back onto the roll, the flexible end covers may be caught between the windings of the roll, which may result in damage to the light-sensitive material. Rewinding the light-sensitive material will hereinafter be called "reverse winding".
Patent application EP-A-0 786 695 discloses a light-tight package for a roll, wherein each end cover consists of an opaque flexible disc, on the outside of which a thin polymer layer of e.g. 30 to 50 .mu.m is extruded. After the extrusion, the polymer layer cools down and shrinks, inducing stresses into the flexible disc, as a result of which the flexible disc is bent to the outside, i.e. towards the extruded polymer layer and away from the roll. The flexible discs are welded to the circumferential cover and to the core.
While this package may solve the problems concerning unsmooth transport and reverse winding, mentioned hereinbefore, it presents several drawbacks. In the first place, it is difficult to control the cooling and the shrinkage process after the extrusion. As a consequence, the magnitude of the induced stresses and of the deformation of the flexible discs may vary widely. This has an adverse effect on the reliability of reverse winding and of smooth transport during unwinding. In the second place, an extra layer, of a heat-resistant lacquer, is required on the extruded polymer layer to prevent the polymer layer from melting when the flexible discs are welded to the circumferential cover and to the core.
Patent application EP-A-0 779 541 solves these drawbacks to a certain extent. It discloses a light-tight package for a roll, wherein each end cover consists of an opaque tearable flexible disc and a rigid disc, the rigid disc being positioned between the flexible disc and the end surface of the roll. The rigid discs have an outer diameter less than or equal to the outer diameter of the roll, while the flexible discs have a larger outer diameter. The outer portions of the flexible discs are folded over the rigid discs and are secured to the circumferential cover of the roll by means of adhesive tape. The adhesive tape and the flexible covers are tearable, and the circumferential cover includes a portion adapted to initiate a tear in the tape and the flexible discs.
However, this package also presents several drawbacks. A first drawback is the presence of tearable adhesive tape, and thus, the risk of contamination with adhesives of the light-sensitive strip material or of the dispensing apparatus. Another drawback is the fact that the flexible discs must be folded over the circumferential cover, which requires an extra step in the packaging process. Further, to initiate a tear in the tape and the flexible discs, the circumferential cover must have a complicated shape; several shapes are illustrated in the patent application.